Itching like hell?

my left thigh is really itchy and red (from my left knee up to my cheek) and its worse when i get in the shower. it's like a rash but it comes and goes: i get in the morning before i get dressed and at night before i go to bed, but not when i'm at school. I'm suspecting fleas, but i haven't seen any bites, and i'm not sure if my cat has been sleeping on my bed (he may have) but i have seen a couple of cat hairs here and there. Any idea of what it could be? (I have changed my bed linens though to see if it goes away)